If every incel somehow got a girlfriend, the net violence in the world would only go up. Because guys who think like this are violent to their girlfriends. It's not their singleness that's dangerous; it's the way they think about women.
One quick glance at any incel gathering place will confirm this. They all have so many violent, terrible fantasies. I'll go so far as I feel sorry for their mental state without condoning how they express that state and they need help. That's their responsibility though.